The invention relates to hinge connection assemblies and particularly to such assemblies which include detent apparatus and apparatus for positioning the members which are hinged together in angular relationship. Although the apparatus will be described primarily in the context of a screen printing apparatus it will be understood that it will have application a to wide variety of other apparatus and the description is intended to illustrate only one application for the invention. The prior art includes U.S. Pat. No. 3,608,854 which issued to the present applicant on Sept. 28, 1971. That patent relates to apparatus which is particularly suitable for releasably and hingably attaching a silk screen frame to a frame support.
The silk screen printing process involves the use of a printing screen mounted in a rectangular screen frame. This frame has side frame members or frame bars which carry means for gripping the screen about its edge and biaxially stretching the screen along the peripheral surface thereof. The actual silk screen printing process is well known and need not be explained here.
The prior art includes a variety of devices for holding the frame which in turn holds the silk screen. Some hinged apparatus has included counter weights to retain the frame in either an open position with respect to a support surface or a closed position proximate to a support surface. Such devices have not been wholly satisfactory because they have not provided the desired accurate positioning of the frame during and following repetitive "opening" and "closing" of the frame relative to the support. Various means have also been provided for spacing the frame from the platen which is a portion of the support surface. Such apparatus has also not been wholly satisfactory because the platen was not adequately stable. Such instability is highly undesirable because it may compromise the quality of the image produced by the silk screen process. The apparatus as generally known previously has also not been sufficiently flexible so that the frame was properly positioned with respect to a relatively wide variety of thicknesses of material on which an image was to be produced. For example, printed circuit boards intended to cooperate with the apparatus in accordance with the invention may vary substantially in thickness, and other members on which an image is to be produced will require an even wider range of operational flexibility because of the still greater variation in thickness of material on which an image is to be produced.
It is a primary object of the invention to provide a hinge assembly which includes a detent assembly for biasing a first hinged member into a predetermined angular relationship with a second hinged member.
Another object of the invention is to provide such apparatus which will in addition also bias the first hinged member into a second predetermined angular relationship with respect to the second hinged member, and the second predetermined angular relationship is different from the first predetermined angular relationship.
Another object of the invention is to provide apparatus which will be convenient to operate.
Another object of the invention is to provide apparatus which will conveniently accommodate materials having a wide range of thicknesses.
Still another object of the invention is to provide apparatus which will provide an absolutely stable mounting of the frame in a silk screen process with respect to the surface on which an image is to be produced.
Yet another object of the invention is to provide apparatus which will repetitively position a hinged member in precise angular relationship with respect to another member.